Conventional ways of gasifying of biomass can utilize thermal methods involving pyrolysis and/or partial oxidation to produce a fuel gas or a synthesis gas composed of carbon oxides and hydrogen. Many of the known methods use a dry biomass feedstock with less than 10 wt % moisture. However, much of the biomass resource that is actually available contains significantly higher levels of moisture, typically 50 wt %. Some biomass even consists of “wet” biomass, or biomass in water slurries at 85 wt % moisture or higher. One approach to efficiently process such wet biomass is gasification employing an active catalyst in a pressurized water environment (e.g., hydrothermal gasification).
However, hydrothermal gasification involving critical, or above critical operating conditions are expensive. Furthermore, when treating wet biomass by hydrothermal gasification, constituents that are commonly inherent in the feedstock can poison and/or foul the catalyst making long-term and/or continuous operation difficult to achieve. Accordingly, a need for improved methods for liquid-phase hydrothermal gasification of wet biomass exists.